Does Art do Marty's part of the story.
Does anyone else think that Hillary and Lea Thompson share appearance factors, and where that could end up for Art/Marty?
And the "Think Tank" can do Doc Brown, all 4 temporal versions simultaneously, 1x19th century (Western), 2x20th century (current and alternate universe versions), and 1x21st century (when the hover gear was installed, and Jaws 15(?) was screening).
... time will tell (pun intended)